For \({\cal Y}\approx 2,-1\)  (but \({\cal Y}\ne 2,-1\) ) the exotic leptons do not mix the SM ones and the lightest state of the spectrum
is electrically charged
and stable due to
exotic lepton number.
Charged relics are cosmologically dangerous and largely excluded. To avoid
cosmological problems one has to invoke low-scale inflation, such that charged relics are
either diluted by inflation or never thermally produced.
On the other hand, stable charged particles yield striking signatures at colliders
in the form of charged track, anomalous energy loss in calorimeters, longer times of flight, etc.
Applying the experimental limits of [1]} at 13 TeV LHC
with the leading-order Drell-Yann cross-sections rescaled for \(|Q|=2\) 
(see also [2]}),
Ref. [3]} obtained \(m_{{\cal N},\, {\cal E}} \gtrsim 800\)  GeV.
Since \(m_{{\cal N},\, {\cal E}} = y_{{\cal N},\, {\cal E}} \, v/ \sqrt{2}\) , direct searches imply Yukawa couplings,
\(y_{{\cal N},\, {\cal E}} \approx 4.6\) ,
at the boundary
of perturbative unitarity (see e.g. [4]}, [5]}).Large higher-order corrections
(starting at two loops) are expected for Higgs decays and they might slightly change the solutions \({\cal Y}\approx 2,-1\) .
